This invention relates to a planetary drive. It relates more particularly to a particularly efficient drive of this type which can be contained within a relatively small package. Planetary drives have of course been available for many years. Many different drive designs have been proposed employing cooperating sets of side-by-side orbiting and nonorbiting gears. Examples of such transmissions are disclosed in the following patents:
U.S. Pat. No. Re. 24,288, Nanni PA1 U.S. Pat. No. 3,056,315, Mros PA1 U.S. Pat. No. 3,073,184, Braren PA1 U.S. Pat. No. 3,192,799, Pamplin PA1 U.S. Pat. No. 3,985,047, Therkelsen PA1 U.S. Pat. No. 3,998,112, Pierrat PA1 U.S. Pat. No. 4,023,440, Kennington PA1 No. 542,206, Fed. Rep. of Germany
Of particular relevance for purposes of this invention are U.S. Pat. Nos. 3,998,112 and 4,117,746, which are owned by the assignee of the present application.
Prior transmissions of this general type employ orbiting gears having teeth or lobes of epitrochoidal curvature which cooperate with surrounding external nonorbiting gears whose teeth are in the form of cylindrical pins or rollers and exceed by one the numbers of teeth in the mating internal orbiting gears. In those drives there are at least two orbiting and nonorbiting gear pairs.
Prior transmissions of that general type are disadvantaged in that the mating orbiting-nonorbiting gear pairs are located side by side so that the gear pairs occupy a relatively large amount of space so that a relatively long housing package is required.
More importantly, however, during operation of the prior transmissions of this type, the forces exerted on the same cam are in opposite directions so that they form a couple. Consequently, those forces tend to cock and skew the bearings required between the orbiting members and their eccentric subjecting them to an excessive amount of stress which accelerates their fatigue and failure.
Also in the prior transmissions, the shaft bearings rotatively supporting the input and output shafts projecting from the housing are relatively remote, being located at the ends of the housing. Consequently, it is relatively difficult to keep them properly lubricated.
Still further, when operating planetary drives of this type as gear pumps in the nature of a geroter pump, it is difficult to maintain the tolerances required to provide effective seals between the mating orbiting and nonorbiting gear surfaces. Consequently, the pumping efficiency of such drives used as pumps is not as high as might be desired.
Further, since the nonorbiting gears in many of the prior drives have teeth in the form of fixed circular arrays of pins, spaced radially outward from the gear axes, maintenance of sufficiently high tolerances between those pins and the bore or barrel through the orbiting gears is difficult to achieve. The result is that the prior units have a tolerance stack-up problem which renders their output motions not as smooth as might be desired. This is particularly so in the case of transmissions subjected to a heavy load which tends to deflect the orbiting gears to the opposite sides of the transmission housing to the extent that their nondriving lobes actually interfere with pins on the opposite sides of the nonorbiting gears.
Also the prior transmission employing pins as the nonorbiting gear teeth are not as efficient as might be claimed or wished. This is because the pins, being rotatably but peripherally restrained in their sockets, are insufficiently lubricated so that a considerable amount of sliding friction exists between the orbiting and nonorbiting gears. Of course, this also promotes excessive parts wear, and subsequently, increases in roughness of operation and noise, a reduced operating life and a general deterioration in efficiency.